High momentum range of electron momentum distributions investigated by means of high energy (e, 2e) collisions

High energy (8̃.5 keV) asymmetric coplanar (e, 2e) experiments are reported for the ionization of the 2s orbital of neon and 4s orbital of krypton. Corresponding electron momentum distributions are measured, with special emphasis being placed on the high momentum range where nodes and secondary maxima are predicted by Hartree-Fock wave functions. The present experimental results are compared with earlier ones at lower impact energy and with the factorized plane wave impulse approximation (PWIA) prediction. They give further evidence for the adequacy of this approximation at small electron momentum values. At high momenta, considerable improvement of the validity of the PWIA is observed with respect to the lower incident energy results, although ejection energy is smaller. Best agreement between experimental data and PWIA prediction is achieved when the scattering angle matches the Bethe ridge of the Bethe surface. The first minimum and secondary maximum of the electron momentum distribution are then experimentally observed for the first time. Trends are discussed in the measured momentum densities with reference to the scattering parameters.